In second language (L2) research and testing, measures of oral fluency are used as diagnostics for proficiency. However, fluency is also determined by personality or speaking style, raising the question to what extent L2 fluency measures are valid indicators of L2 proficiency. In this study, we obtained a measure of L2 (Dutch) proficiency (vocabulary knowledge), L2 fluency measures, and fluency measures that were corrected for first language behavior from the same group of Turkish and English native speakers (N = 51). For most measures of fluency, except for silent pause duration, both the corrected and the uncorrected measures significantly predicted L2 proficiency. For syllable duration, the corrected measure was a stronger predictor of L2 proficiency than was the uncorrected measure. We conclude that for L2 research purposes, as well as for some types of L2 testing, it is useful to obtain corrected measures of syllable duration to measure L2-specific fluency.